Microwave antenna system



Sept 3, 1957 B. BERKOWITZ 2,805,415

' MICROWAVE ANTENNASYSTEM Filed Aug. z 1952 TTORNEY United States Patenttice Patented Sept. 3, 1957 MICROWAVE ANTENNA SYSTEM Bernard Berkowitz,Jamaica, N. Y., assignor to Sperry Rand Corporation, a corporation ofDelaware Application August 2, 1952, Serial No, 302,401 8 Claims. (Cl.343-777) This invention relates to a microwave antenna system, and, moreparticularly, is concerned with a horn structure for sequentiallyproducing asymmetrical electromagnetic radio beams having space patternswhich are mir-' ror images of one another.

Transmitting systems providing alternately energized overlapping lobesare employed in aircraft locators, direction finders, and instrumentlanding systems. Particularly in the latter case, it is desirable thatthe individual eld patterns of the overlapping lobes have anasymmetrical conguration to provide broad coverage in the offcourseregion and to provide sharp cut-off in the oncourse region where thelobes overlap, the two lobes having space patterns which aresubstantially mirror images of each other.

It is a general object of this invention to provide an improvedradiating system for producing overlapping lobes having asymmetricalspace patterns.

Another object of this invention is to provid-e means, including a horntype radiator, which can be readily controlled and adjusted to modifythe space pattern of each of the lobes.

Another object of this invention is to` provide a radiat ing system inwhich the shape of the farfeld pattern can be modified withoutphysically altering the radiating structure by simply changing the phaserelationship and power level of the energy components fed to theradiator.

Another object of this invention is the provision of a radiator capableof producing a pair of overlapping asym- Y metrical lobes from acontinuously energized compoundtype horn.

These and other objects of the invention which will become apparent asthe description proceeds are achieved by the provision of a radiatorcomprising a single sectoral horn mounted above a pair of adjacentsectoral horns, the apertures of these horns lying in a commonplane. Themouth of the single sectoral horn is joined to and feeds energy to a rstinput wave guide section of a Y-junction. The mouths of the adjacenthorns are joined as a pair and feed energy to a second input wave guidesection of the Y-junction, the wave guide sections of the junctionhaving the same cross-sectional dimensions as the mouth of the firsthorn and the combined mouths of the adjacent horns. The output Waveguide section of the Y-junction is connected to an output sectoral hornwhich is ared in a plane perpendicular to that of the above-mentionedhorns. Microwave energy is fed to each of the pair of adjacent horns inphase opposition with respect to the other, and in phase quadrature withrespect to the` microwave energy fed to the single horn. Switching meansis provided which introduces a periodic phase reversal in the energy fedto the pair of horns in relation to the energy in the single horn toprovide sequential mirror image asymmetrical space patterns.

For a better understanding of the invention reference should be had tothe accompanying drawings, wherein,

Fig. l is a plan View of the radiating structure of the presentinvention;

Fig. 2 is a side elevational view of the radiator system;

Fig. 3 is a graphical plot of the `electric field intensity as afunction of position across the aperture of the single horn and the pairof adjacent horns; and

Fig. 4 is a rectangular coordinate plot of the resulting far-field spacepattern showing the energy measured in decibels as a function of angulardeviation from a line perpendicular to the plane of the horn aperture.

With particular reference to the Vform of the invention as illustratedin the drawings, the numeral 10 indicates generally a source ofmicrowave energy, such as, for example, the transmitter of an instrumentlanding system. Energy from the microwave source 10 is coupled to theinput portion of an adjustable divider 11, which may be of any suitabletype such as a hollow pipe wave guide Y-junction having a movable ap 12for changing the ratio of energy transmitted through the two outputportions. An adjustable phase shifter 15 and a rectangular hollow waveguide` 13 couple energy from the upper output portion of the divider 11to a sectoral horn 14. The sectoral horn 14 is joined at its throatportion 16 to the wave guide 13.

Mounted directly below the sectoral horn 14 and in adjacent relationshipto each other are a pair of sectoral horns 20 and 22 Whose respectiveapertures 24 and 26 lie in a common plane with the aperture 18 of thesectoral horn 14. The throat portions of sectoral horns 20 and 22,indicated at 28 and 30 respectively, are joined by a rectangular hollowwave guidesection 32. Energy from the lower output portion of thedivider 11 is fed to the` sectoral horns 20 and 22 through a phaseswitch, indicated` generally at 19 (the form and function of which ishereinafter described), to an E-plane` T 36 in the wave guide 32 at a point mid-way between the throat portions 28 and 30 of the sectoral horns20 and 22. By virtue of the additional path length, equal to a halfwavelength at the operating frequency, provided by the loop 33, theelectric field at any given point in the horn 20,. for example, at theaperture 24, is out of phase with the electric eld in the horn 2,2 atthe corresponding point,` as at the aperture 26.

The instantaneous far-eld pattern generated by the multiple hornstructure above described may be considered as made up of twocomponents, hereinafter referred to as thesymmetric component and theanti-symmetric component. The symmetric component is radiated from thesingle horn 14 while the anti-symmetric component is radiated from thepair of adjacent horns 20 and 22 acting simultaneously. When the energyilluminating the single horn aperture 18 is in phase quadrature withrespect to the energy illuminating the coplanar double apertures 24, 26,the far-field pattern generated is the algebraic sum of the componentpatterns. The phase quadrature relationship may be obtained by providinga difference in path length of a quarter of a wavelength between thetransmission path from the source 10 to the aperture of the horn 14 andthe transmission path from the source 10 to the apertures of the horns20 and 22. The, phase shifter 15 provides additional adjustment toachieve theI desired phase relationship. By proper selection of hornshape, including the ilare angle, length of the horn, and formation ofthe throat portion where the horn is joined to the input wave guide, theenergy distribution across` the aperture of any of the horns can becontrolled. The

illumination that the far-field pattern of the horn follows` the samefunction. Thus, the` symmetric component of the far field is aGaussian-like patter The horns 20 and 22 are preferably designed" sothat,`

when energized 180 out of phase with each other, the illumination acrossthe adjacent apertures 24 and 26 resembles approximately a Rayleighfunction, which is the derivative of the Gaussian function; Theillumination across the`combined apertures 24 and 26 is illustrated bycurve 40 of Fig. 3. An aperture illumination' resembling thelRayleighfun-ction likewise produces a far-eld pattern -following thesame function. Thus, t-he anti-symmetric component of the far-fieldVpattern is a Rayleighlike pattern. Moreover, the sum of these functionsat the aperture of a horn, regardless of the ratioof energy levelstherein, yields a space pattern resembling the algebraic sum of thecomponents. With the horn apertures having an energy distributionaccording to the Gaussian and Rayleigh functions, the far-field patterncan be readily found by adding algebrai- 'callyrthe two curves 38 andl40ct Fig. 3, which also represent t-he far-field component patterns.The result is an asymmetrical space pattern, as Vshown by the curve 42of Fig. 4, obtained vby the addition of the symmetrical andAanti-symmetrical components which 'are derived respectively from the4single horn 14 and the adjacent horns 20 and 22. u It will beappreciated -that the energy distrirbution in the far-eld Vpattern ispartly affected by the power ratio of the symmetric and anti-symmetriccomponents. Thus, the present invention provides a ready means forvarying t-he shape of the pattern in space simply by regulating thispower ratio, which can be accomplished by means of the adjustabledivider 11.

By reversing the phase of the energy in the -horns 20 and 22,thealgebraic sign of the anti-symmetric component of the far-fieldpattern is changed, as indicated by therdotted curve 40', of Fig. 3. Thedotted curve 42 of l'ig. 4 indicates the resulting pattern in space, andis a mirror image of t-he pattern 42 resulting from the antisymmetriccomponent of curve 40. This 180 phase shiftl is periodically introducedby the switch 19, which alternately permits passage of energy throughwave guide sections 44 and 46. These sections differ in path length by ahalf guide wavelength. One suitable switch for such purposes includes amotor 48 which drives a disc 50, the disc Ibeing provided around itsperiphery with a plurality of spokes. The spokes pass through gaps ineach of the wave guide sections 44 and 46, and are so positioned thatwhen a spoke intercepts one of the wave guidel sections, the other waveguide section is open to permit transmission of energy therealong. Aswitch of this type is described in detail in Patent No. 2,544,715 to R.B. Muchmore.

In order to avoid phase interferences in the elevational andthe horns 20and 22 are combined and radiated from a single aperture. This isaccomplished by the provision of a Y-junction wave guide section,indicated generally at 52, the branch arms 54 and 56 of which join thesingle lliorn14and the adjacent horns 20v and 22 at their respectiveapertures. The output portion 58 of the Y- junction 52 is narrowed inthe E-plane to attenuate higher order modes which might be produced inthe Y-junction. The output portion 58 is coupled to the throat of anoutput sectoral horn 59 which provides beam sharpness in elevation. TheilareV of the output horn 59 is perpendicular tothe flareV ofthefsectoral horns 14, 20 and 22.

To improve the operation of the radiating system,impedan'celmatching-between the sectoral horns 14, 2i) and 22 and theY-junction 52 is desirable. Thus matching irises formedby the projectingmember '60 in each of the wave v'guide input portions 54 and 56 of theY-junction 52 may be provided. Y A radio energy absorbent material 62 ispreferably used asa lining for the inner surfaces of vthe,` sectoralhorns to attentuate energy reected from the Y-junction 52 and to reduceintercoupling ,of'energy between the horns. Y e the `radiating systemdoes; not require that the E-vector in ItV should be noted thattheoperation of 4 the horns be aligned in any particular direction, i.e., the horns may be flared in either the E-plane or the H-plane.

While the horns 14, 20 and 22 have been described :as preferablygenerating aperture illuminations following Gaussian and Rayleighfunctions, it should berunderstood that it is not essential `to ltheoperation of the present invention that the energy distribution belimited tothese funcions only. They merely provide a ready basis forpredicting the far-field pattern because of their self-reciprocallproperties as above described. However, farifield patterns of variousconfigurations can be generated by providing other apertureilluminationv functions from lthose described. Y

While the aperture 18 hasl been illustrated as having a width Ithatsubstantially equals that of the combined apertures 24 and 26, suchrelationship is not essential to the operation ofthe present invention,and in fact, a slightly narrower aperture in the single horn 14 may bedesirable to limit side` lobe effect. be noted that lenses may be usedVin combination with the horn structure above described to provideadditional shaping of the far-held pattern as may be required.

VFrom the above description, it will be appreciated that Ithe objects ofthe invention have been 'achieved by the provision of a radiating systemwhich produces asymrnetricall overlapping lobes in space by the use of acoutinuously energized compound-type horn structure. Considerablelatitude is provided in shaping the far-field pat- Y low pipe wave guidecoupling the source -to said` pair of tern simply by modifying the powerlevel and phase rela.

tionship of the energy components of the radiatingsystem by means of thedivider 11 and phase `shifter 15.

It should be noted that, although the present invention has beenparticularly described as a radiating system, it may be readily adaptedfor use as a directional receiving system .as well. A the aboveconstruction and many aparently widely different embodiments of thisinvention Vcould be made without departing from the scope thereof,it isintended that all matter contained in the above description or Yshown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense. Y

What is claimed is: t g

1. Ultra high frequency apparatus comprising a single sectoral horn, avpair of sectoral horns having their apertures 'in a common plane withthe aperture of said single sec-toral horn, Ithe apertures of saidpairfof sectoral horns being in line and adjacent each other andparallel to the aperture of said single sectoral horn, a source ofmicrowave energy, a hollow pipe wave guide coupling the source to saidsingle sectoral horn, a Vbifurcated holsectoral horns, said bifurcatedwave guide transmitting energy -to `the pair of sectoral horns in phaseopposition to each other, means including a microwave Vswitch in serieswith'one of the wave guides for periodically Y shifting -the phase yofthe energy in'one of the Vwave guides horn, the other of said inputsections being joined to and coeXtensive with the-combined adjacentapertures of said pair of horns, the energy from said single sectoral?,horn being in phase quadrature with respect toy energy from said pair ofsectoral horns-in the output wave guide.

section, and an `output sectoral horn ilared in a plane perpendicular tothe flare-plane of said single and saidrpair of sectoralhorns,.theroutput section ofthe Y-junction being joined to the throatportion of said output horn.

2. Ultra high frequency Vapparatus comprising a single sectoral horn, apair of sectoral horns having their apertures in a common plane wi-ththe apertureof said singlev sectoral horn, thenapertures of said pair ofsectoral horns being in lline andV adjacent each other andV parallel tothe,

In addition, it should n Since many changes could be made in aperture ofsaid single sectoral horn, a source of microwave energy, means couplingthe microwave source to each of said sectoral horns, said means couplingenergy to said pair of horns in phase opposition with respect to eachother, means for periodically changing the relative phase of the energyin said single lhorn and said pair of horns by 180, means including apair of input hollow pipe wave guide sections and an output wave guidesection joined in a Y-junction, one of said input sections being joinedto and coextensive with the aperture of said single horn, the other ofsaid input sections being joined to and coextensive with the combinedadjacent apertures of said pair of horns, the venergy from said singlesectoral horn being in phase quadrature with respect to energy from saidpair of sectoral horns in the wave guide output section, and an outputsectoral horn flared in a plane perpendicular to the areplane of saidsingle and said pair of sectoral horns, the output section of theY-junction being joined to the throat portion of said output horn.

3. Ultra high frequency apparatus comprising a single sectoral horn, apair of sectoral horns having their apertures in a common plane with theaperture of said single sectoral horn, the apertures of said pair ofsectoral horns being in line and adjacent each other and parallel to theaperture of said single sectoral horn, a source of microwave energy, ahollow pipe wave guide coupling the source to said single sectoral horn,a bifurcated hollow pipe wave guide coupling the source -to said pair ofsectoral horns, said bifurcated wave guide transmitting energy to eachof said pair of sectoral horns in phase opposition, means in series withone of the wave guides for periodically shifting the phase of the energyin one of the wave guides relative to the phase in the other of ythewave guides by 180, means including a pair of input hollow pipe waveguide sections and an output wave guide section joined in a Y-junction,one of said input sections being joined to and coextensive with the`aperture of said single horn, -the other of said input sections beingjoined to and coextensive with the combined adjacent apertures of saidpair of horns, and an output sectoral horn joined at the throat portionthereof to the output section of the Y-junction.

4. Ultra high frequency apparatus comprising a single sectoral horn, apair of sectoral horns having their apertures in a common plane with theaperture `of said single sectoral horn, the apertures of said pair ofsectoral horns being in line and adjacent each other and parallel to theaperture of said single sectoral horn, a source of microwave energy, ahollow pipe wave guide coupling the source to said single sectoral horn,a bifurcated hollow pipe wave guide coupling the source to said pair ofsectoral horns, said bifurcated wave guide transmitting energy to saidpair of sectoral horns in phase opposition to each other, means inseries with one yof the wave guides for periodically shifting the phaselof the energy in one of the wave guides relative to the phase in theother ofthe wave guides by 180, and an output sectoral horn ared kin aplane perpendicular to the Hare-planes of said single and said pair ofsectoral horns, and means coupling energy to the throat portion of ytheoutput sectoral horn from the apertures of said single sectoral horn andsaid paid of sectoral horns.

5. Ultra high frequency apparatus comprising a single sectoral horn, apair of sectoral horns having their apertures in a common plane with theaperture `of said single sectoral horn, the apertures of said pair ofsectoral horns being in line and adjacent each other and parallel 4tothe aperture of said single sectoral horn, a source of micr0- waveenergy, a hollow pipe wave guide coupling the source to said singlesectoral horn, a bifurcated hollow pipe wave guide coupling the sourceto said pair of sectoral horns, the energy at the aperture of saidsingle sectoral horn being in phase quadrature with respect to energy atthe apertures of said pair of sectoral horns, said bifurcated wave guidetransmitting `energy to said pair of sectoral horns in phase oppositionto each other, and means including a microwave switch in series with oneof the wave guides for periodically shifting the phase of the energy inone of the wave guides relative to the phase in the other of the waveguides by 6. Apparatus for radiating asymmetrical mirror image lobes,said apparatus comprising a microwave source, a single horn, a pair ofhorns in side-by-side relationship and radiating from a single aperture,means coupling each of the horns to the microwave source, said meanscoupling energy to the single horn in phase quadrature with respect toenergy coupled -to said pair of horns, said means further couplingenergy to said pair of borns in phase opposition with respect to eachother, and switching means in series with said coupling means andadap-ted to periodically change the relative phase of :the energy in thesingle horn and the pair of horns by 180.

7. Apparatus for generating consecutively a pair of asymmetricaloverlapping radio beams, said apparatus comprising rst horn meansradiating a symmetrical component, second horn means radiating ananti-symmetrical component, said first and second horn means radiatingen ergy from a common aperture, the energy from said iirst horn meansbeing in phase quadrature with respect to the energy from said secondhorn means at said common aperture, and means for periodically changingthe relative phase of the energy from said rst horn means and from saidsecond horn means at the common aperture by 8. Apparatus for generatingconsecutively a pair of asymmetrical overlapping radio beams, saidapparatus comprising iirst horn means radiating a symmetrical component,second horn means radiating an anti-symmetrical component, and means forperiodically changing the relative phase of the energy from said firsthorn means and from said second horn means.

References Cited in the le of this patent UNITED STATES PATENTS2,415,242 Hershberger Feb. 4, 1947 2,438,735 Alexanderson Mar. 30, 19482,438,987 Bailey Apr. 6, 1948 2,461,005 Southworth Feb. 8, 19492,482,162 Feldman Sept. 20, 1949 2,514,678 Southworth July 11, 19502,540,839 Southworth Feb. 6, 1951 2,556,094 Lindenblad June 5, 19512,627,020 Parnell et al J an. 27, 1953

